The present invention relates to a paper feeding mechanism in a printer.
In a heretofore proposed printer such as a register printer, for example, a receipt paper and a journal paper are provided in juxtaposed relationship to each other and are printed simultaneously so that the printed receipt paper is delivered to a customer while the printed journal paper is wound up on a reel for the record of the printed data. In such a printer, it may be required to feed either of the receipt paper and the journal paper independently from each other. The paper feeding mechanism in such a printer comprises in general a set of a paper feeding roller and a pressure roller cooperating therewith for each of the receipt paper and the journal paper so as to feed the paper sandwiched therebetween by the action of the paper feeding roller. Thus, two sets of paper feeding mechanism are required which are actuated independently from each other, thereby rendering the construction to be very complicated.
Alternatively, a register printer may comprise a common paper feeding roller for both the receipt paper and the journal paper and a pressure roller exclusively for the receipt paper or the journal paper each normally held apart from the paper feeding roller is selectively urged against the paper feeding roller when the selected one of the papers is to be fed.
In this case, the paper located between the feeding roller and the pressure roller which is held apart from the paper feeding roller under the inactive condition of feeding of the paper is free so that it is liable to be shifted even though the pressure roller is held apart from the paper feeding roller which is rotated so as to feed the other paper by the cooperation with the pressure roller for that paper to be fed, the shifting of the paper thereby resulting in erroneous printing operation.
In a printer of the type described above, the receipt paper and the journal paper are in general supplied from respective supply rolls of paper arranged in the printer and each of the papers is selectively unwound from the roll of paper by the paper feeding mechanism belonging to that roll. Since the amount of the paper in each roll is reduced as the paper is unwound therefrom for the printing operation, it is required to provide a detecting device for preventing false printing operation due to failure of supply of paper which might be caused after the paper of the roll has been used up.
Heretofore proposed detecting device comprises a swingable detecting lever with one free end resiliently urged against the peripheral surface of the roll so as to sense the diameter or the radius of the roll which corresponds to the amount of the paper remaining in the roll, while the other free end cooperates with a switch connected to a control circuit of the printer so that the switch is actuated so as to stop the operation of the printer when the swingable lever senses the diameter or the radius reaching a predetermined value for stopping the operation of the printer in order to prevent the false printing operation. In such a prior art detecting device, the rate of reduction of the diameter or the radius of the roll is very low so that the point of actuation of the switch is rendered to be unstable and, since the switch is gradually actuated to be closed or opened, electric noise tends to be generated. Further, since the detecting lever follows the peripheral surface of the roll intermittently rotated as the paper is fed there from so that vibration of the detecting lever is caused so as to repeat the closing and opening of the switch thereby generating chattering of the switch. Further, the range of actuation of the detecting lever must be increased as the diameter of the roll is increased, thereby requiring a large detecting lever which in turn increases instability of the actuation of the switch.
The present invention aims at avoiding the above described disadvantages of the prior art paper feeding mechanism of a printer.